Answer: C) This is the flag designer of whom I have spoken.
Step-by-step explanation: A relative pronoun is a type of pronoun that often introduces dependent clauses (phrases that don't have complete meaning on their own) in sentences. The relative pronouns are: who, whoever, whom, whomever, that, which, when, where, and whose. From the given options the sentence that has a relative pronoun within the object of a preposition is "This is the flag designer of whom I have spoken" the preposition is "of" and the relative pronoun is "whom."